As a driving power source of a vehicle and the like, a battery is used to supply electric power to an electric motor. As a battery, for example, a secondary battery such as a lead storage battery and a lithium ion battery is employed. In addition to the battery, an apparatus capable of charging or discharging electric energy using an electric double-layer capacitor and the like is also known in the art.
Although the battery has a large storable capacity, its service lifespan is shortened when the charging/discharging is performed very frequently or in a deep cycle. In comparison, the capacitor is resistant to such frequent charging/discharging or a deep cycle and has a long service lifespan. However, the capacitor has a small storable capacity. In this manner, characteristics are different between the battery and the capacitor. Therefore, if both the battery and the capacitors are mounted together, it is necessary to perform a control in consideration of each characteristic.
In JP 2008-035670 A, there is disclosed a technique of guaranteeing an electric charging capacity of an electric charging mechanism having output performance superior to others in a vehicle provided with a plurality of electric charging mechanisms including both a battery and a capacitor.
In JP 2007-223458 A, there is disclosed a technique of using a subsidiary battery without a voltage converter to drive electric accessories such as a pump, a motor, and a fan.